How do I add digits to all numbers in a column?

[MysticalWaters79]

I have a large database of phone numbers. some are 10 digits, and some are
only 7. I need all numbers that are 7 digits to have the same area code
added to the front. Is there a way to do this other than manually?

 

[T. Valko]

What format are the phone numbers in?

Show us both a 10 digit number and a 7 digit number.

 

[Fred Smith]

I would create a new column with the new numbers in them. How you convert
them depends on how your numbers are store. If they are straight text, you
can use something like:
=if(len(a1)=10,A1,"306"&a1)

If they have some other format, you can adapt the above, or post back with
details.

Regards,
Fred